7th Science - First Term Exam 2024 - Solutions
I. Choose the appropriate answer. (10x1=10)
1. SI unit of density is __________.
b) Kg/m³
2. Light year is the unit of __________.
a) distance
3. A particle is moving in a circular path of radius 'r'. The displacement after half a circle would be __________.
c) 2r (Displacement is the diameter of the circle).
4. The metal which is liquid at room temperature is __________.
c) mercury
5. The sub-atomic particle which revolves around the nucleus is __________.
c) electron
6. Vegetative propagation by leaves takes place in __________.
a) bryophyllum
7. Climbing roots are seen in __________.
c) Both of them (Both betel and black pepper are climbers with climbing roots).
8. Sleep is not only good for our body, but it is also good for, __________.
c) mind
9. Tobacco chewing causes __________.
b) periodontitis
10. Which of the following is an example for animation?
c) Vector communication (Refers to vector graphics, a fundamental technology for creating 2D animation).
II. Answer any 15 questions: (15x2=30)
11. Define - Astronomical unit.
An Astronomical Unit (AU) is defined as the mean distance between the center of the Earth and the center of the Sun. 1 AU ≈ 149.6 million kilometers.
12. Fill in the blanks
a) Density of mercury is 13,600 kg/m³.
b) One cubic metre is equal to 10,00,000 cubic centimetre.
13. Analogy.
a) Velocity : metre / Second :: Acceleration : metre / second² (m/s²)
b) Length of scale : metre :: Speed of aeroplane : Knot or km/h
14. Distinguish between speed and velocity.
- Speed: It is the rate of change of distance. It is a scalar quantity, having only magnitude.
- Velocity: It is the rate of change of displacement. It is a vector quantity, having both magnitude and direction.
15. What are compounds? Give two examples.
A compound is a pure substance formed when two or more elements are chemically combined in a fixed ratio by mass.
Examples: Water (H₂O), Carbon dioxide (CO₂).
16. Define the following terms with an example for each.
a) Element: A pure substance that consists of only one kind of atom. Ex: Iron (Fe).
b) Compound: A substance formed by the chemical combination of two or more elements. Ex: Sodium Chloride (NaCl).
c) Metal: An element that is typically hard, shiny, malleable and a good conductor of heat and electricity. Ex: Copper (Cu).
d) Non-metal: An element that is typically dull, brittle and a poor conductor of heat and electricity. Ex: Sulphur (S).
e) Metalloid: An element that has properties intermediate between metals and non-metals. Ex: Silicon (Si).
17. Match the following:
a) Valency - Electrons in the outermost orbit
b) Neutral particle - Neutron
c) Iron - Fe
d) Hydrogen - Monovalent
18. State true or False. If false, correct the Statement.
The nucleus is surrounded by protons.
False.
Correct Statement: The nucleus is surrounded by electrons.
19. Match the following:
a) Petal - Attracts insect
b) Fern - Spore
c) Hooks - Bignonia
d) Phylloclade - Opuntia
20. What is cross pollination?
Cross-pollination is the transfer of pollen grains from the anther of a flower to the stigma of a genetically different flower, i.e., a flower on another plant of the same species.
21. What are the two important parts of a flower?
The two important (essential) parts of a flower are the Androecium (male reproductive part) and the Gynoecium (female reproductive part).
22. Fill in the blanks:
a) I am green colour box with garbage. I am a green dustbin (for biodegradable waste).
b) Tuberculosis is caused by the bacterium Mycobacterium tuberculosis.
23. What is hygiene?
Hygiene refers to conditions and practices that help to maintain health and prevent the spread of diseases. It includes personal cleanliness and maintaining clean surroundings.
24. Name the mode of transmission of communicable diseases.
Communicable diseases are transmitted through:
- Direct contact
- Air (droplet infection)
- Contaminated food and water
- Vectors (insects like mosquitoes)
25. Define: Mastication
Mastication is the process of chewing food with the teeth in the mouth. It breaks down food into smaller particles and mixes it with saliva to begin digestion.
26. Write a note on 2D and 3D pictures.
2D (Two-Dimensional) pictures: These have only two dimensions: length and width. They appear flat. Examples: Drawings on paper, photographs.
3D (Three-Dimensional) pictures: These have three dimensions: length, width, and depth. They create an illusion of depth and look realistic. Examples: Sculptures, 3D movies.
27. Differentiate mass number from atomic number.
Atomic Number (Z): It is the number of protons present in the nucleus of an atom. It is unique for each element.
Mass Number (A): It is the total number of protons and neutrons present in the nucleus of an atom.
28. Define, molecule.
A molecule is the smallest particle of an element or a compound that can exist independently and shows all the properties of that substance. It consists of two or more atoms chemically bonded together.
29. What is Centre of gravity?
The center of gravity of an object is the point through which the entire weight of the object appears to act, regardless of the object's orientation.
30. Define Stability.
Stability is the ability of an object to maintain its original position. An object is stable if its center of gravity is as low as possible.
III. Answer all the questions (4x5=20)
31. a) How will you determine the density of a stone using a measuring Jar?
- Measure the mass: First, find the mass (m) of the stone using a physical balance. Let the mass be 'm' grams.
- Measure the initial volume: Take a measuring jar and pour some water into it. Note the initial volume of the water (V₁).
- Immerse the stone: Tie the stone with a thread and gently lower it into the measuring jar until it is fully submerged.
- Measure the final volume: The water level will rise. Note the final volume of the water with the stone in it (V₂).
- Calculate the volume of the stone: The volume of the stone is the difference between the final and initial readings. Volume (V) = V₂ - V₁.
- Calculate the density: Use the formula for density:
Density (ρ) = Mass (m) / Volume (V). The unit will be g/cm³.
b) Explain the types of Stability with suitable examples?
- Stable Equilibrium: An object is in stable equilibrium if it returns to its original position after being slightly displaced. In this state, the center of gravity is at its lowest possible position. When displaced, the center of gravity is raised.
Example: A cone resting on its base. - Unstable Equilibrium: An object is in unstable equilibrium if it does not return to its original position after being slightly displaced and instead topples over. In this state, the center of gravity is at its highest position. When displaced, the center of gravity is lowered.
Example: A cone balanced on its vertex (tip). - Neutral Equilibrium: An object is in neutral equilibrium if it remains in the new position after being displaced. The height of its center of gravity remains constant.
Example: A ball rolling on a horizontal surface.
32. a) Differentiate metals and non-metals?
| Property | Metals | Non-metals |
|---|---|---|
| State | Usually solid at room temperature (except Mercury). | Exist as solids, liquids, or gases. |
| Lustre | Have a shiny surface (lustrous). | Have a dull surface (non-lustrous). |
| Malleability | Can be beaten into thin sheets (malleable). | Brittle and break when hammered. |
| Ductility | Can be drawn into wires (ductile). | Cannot be drawn into wires (non-ductile). |
| Conductivity | Good conductors of heat and electricity. | Poor conductors of heat and electricity (except graphite). |
| Examples | Iron, Copper, Gold | Sulphur, Oxygen, Carbon |
b) Draw the structure of an atom and explain the position of the sub-atomic particles.
An atom consists of a central nucleus and electrons that orbit the nucleus. The positions of the sub-atomic particles are:
- Protons: They are positively charged particles located inside the nucleus at the center of the atom.
- Neutrons: They are neutral particles (no charge) also located inside the nucleus along with the protons.
- Electrons: They are negatively charged particles that revolve around the nucleus in specific, fixed paths called orbits or shells.
33. a) Explain the underground stems.
Types of Underground Stems:
- Rhizome: It is a thick, horizontal stem that grows beneath the soil. It has nodes, internodes, and scale leaves. Example: Ginger, Turmeric.
- Tuber: It is the swollen, fleshy tip of an underground stem branch. It stores food as starch and has buds called 'eyes'. Example: Potato.
- Bulb: It is a condensed underground stem with a terminal bud and fleshy scale leaves that store food. Example: Onion, Garlic.
- Corm: It is a short, swollen, upright, underground stem that stores food. It has a solid, fleshy structure. Example: Colocasia.
b) Write a brief account on Pollination.
Pollination is the process of transferring pollen grains from the anther (male part) to the stigma (female part) of a flower.
Types of Pollination:
- Self-Pollination (Autogamy): The transfer of pollen grains from the anther to the stigma of the same flower or another flower on the same plant.
- Cross-Pollination (Allogamy): The transfer of pollen grains from the anther of a flower on one plant to the stigma of a flower on another plant of the same species.
Agents of Pollination:
Pollination is carried out by various agents, which can be biotic (living) or abiotic (non-living).
- Abiotic agents: Wind (Anemophily), Water (Hydrophily).
- Biotic agents: Insects (Entomophily), Birds (Ornithophily), Bats (Chiropterophily).
34. a) Write about any three communicable disease?
- Tuberculosis (TB): It is an infectious disease caused by the bacterium *Mycobacterium tuberculosis*. It primarily affects the lungs. It spreads through the air when an infected person coughs or sneezes. Symptoms include a persistent cough, fever, and weight loss.
- Cholera: It is an acute diarrhoeal disease caused by the bacterium *Vibrio cholerae*. It spreads through contaminated food and water. It leads to severe dehydration and can be fatal if not treated promptly.
- Common Cold: It is a viral infectious disease of the upper respiratory tract. It is caused by rhinoviruses and spreads through airborne droplets or direct contact with infected objects. Symptoms include a runny nose, sneezing, and sore throat.
b) How the diseases are transmitted from person to the other person?
- Direct Contact: Transmission through physical contact with an infected person, such as touching or kissing. E.g., Chickenpox.
- Indirect Contact: Transmission through contact with contaminated objects (fomites) used by an infected person, like utensils, clothes, or doorknobs.
- Through Air (Droplet Infection): Pathogens are spread through droplets released into the air when an infected person coughs, sneezes, or talks. E.g., Common Cold, Tuberculosis.
- Through Contaminated Food and Water: Consuming food or water that has been contaminated with pathogens. E.g., Cholera, Typhoid.
- Through Vectors: Organisms like mosquitoes, flies, and ticks can carry pathogens from an infected person to a healthy person. E.g., Malaria is transmitted by mosquitoes.